In the logging industry, the tractors used to haul logs and move logging machinery from place to place regularly encounter ground conditions so bad that wheel traction is very uncertain. This is true even though very large tires with non-skid treads are used.
Accordingly, it has been customary to apply to the tires large size anti-skid traction units (known as skidders or skidder rings) which are held in place on the tires by heavy duty tag chains, connecting chains and side chains. In spite of the heavy duty chains that are used, the extreme conditions to which the equipment is subjected result in occasional chain breakage. The most common chain breakage occurs in the tag chains that connect the skidders. The tag chains come into direct contact with the ground as the wheel rotates, resulting in continuous and ralatively rapid wear.
In the construction of the skidders now in general use, there are four eyes in which the end links of the tag chains are placed and secured by welding the eye or the end link in closed position. To replace a broken tag chain, it is necessary to perform a welding operation which usually is difficult to do under the normal working conditions in the woods. If the repair cannot readily be made at the site, then the entire traction unit must be removed from the wheel to be replaced by another complete unit, if available.